He made a modular, 3D printed tilting-rotor drone - vertical takeoff/landing but with fixed wings like an airplane for range/efficiency. Other VTOL fixed wings have twice as many motors, with a pair of motors being idle at any time, because the motors don't tilt.
I did a report of titling-rotor aircraft in high school - iirc they never really became a thing because they were too complex. Drones might flip the script on that. Although, I've seen jet powered, fixed wing drones do VTOL without rotors which land on their tail, vertically. I wonder if this design could be improved by doing something similar with rotors.
Also, if you can 3D print most of a drone, it might be time to get a 3D printer.